The present invention is directed to an arrangement for DPCM-coding with high data rates.
An arrangement for DPCM coding that, for example, is known from Proc. IEEE, Vol. 73, No. 4, April 1985, pages 592 through 598, particularly FIGS. 1, 2 and 4 therein, is set forth with reference to a fundamental circuit diagram shown in FIG. 1. A sequence of digitized picture element signals s is received at an input 1, these signals s being supplied via sample and hold stages that are not shown in detail. In order to reduce the data flow, an effort is made to remove redundant and irrelevant parts of the picture signal in order, for example, to be able to lower the bit transmission rate without thereby deteriorating the image quality. In detail, this occurs in that it is not the successive picture element signals that are transmitted via the transmission channel leading to a reception location, but rather, only the difference signals that are formed by taking the difference between a respectively current picture element signal s and a prediction value s calculated on the basis of the preceding picture element signals which are transmitted. Such a method is also referred to as difference pulse code modulation (DPCM).
According to FIG. 1, the difference formation required for a DPCM-coding is carried out in a subtractor 2 whose first input is connected to the input 1 and whose second input is connected to a predictor 3. Every difference signal .DELTA. that is also referred to as prediction error is quantized in a quantizer 4, whereby the difference signal .DELTA. q=.DELTA.+q affected with the quantization error q is coded in a coder 5 and is supplied to the transmission channel via an output 6. A recursive signal path is provided for forming the prediction value s, this signal path connected from a circuit point 7 at the output side of the quantizer 4 to the second input of the subtractor 2. The signal path contains a first adder 8, a limiter means 9 and the predictor 3. The output of the predictor 3 is also connected to a second input of the first adder 8 that forms what is referred to as a reconstructed picture element signal s.sub.r by addition of the quantized difference signal .DELTA. q and the prediction value s. The predictor 3 supplies the prediction value s from at least one of the preceding picture element signals for every current picture element signal s.
When, according to FIG. 2, the current picture element lying in the line n in a video picture m is referenced X, the picture element sampled immediately therebefore is referenced A, the picture element of the preceding line n-1 corresponding to X is referenced C and the picture elements neighboring the latter and sampled immediately before or after that are referenced B and D and when, further, the corresponding picture elements of the preceding picture m-1 are referenced X' and A' through D', the following then results: the picture element signals of at least one of the points A through D can be utilized for the formation of the prediction value s for the picture element signal of X, whereby one speaks of a two-dimensional (2D) prediction. When the picture element signals of at least one of the picture elements X' and A' through D' are used exclusively or in addition thereto, then there is a three-dimensional (3D) prediction. In the former instance, the prediction value s can, for example, be calculated according to the 2D estimation equation: EQU s=.alpha..multidot.s.sub.A +.beta..multidot.s.sub.B +.gamma..multidot.s.sub.C +.delta..multidot.s.sub.D
In the latter instance, for example, the prediction value s can be calculated according to the 3D estimation equation: s=.alpha..multidot.s.sub.A +.beta..multidot.s.sub.X, whereby s.sub.A references the reconstructed picture element signal of the picture element A, s.sub.B references that of the picture element B, etc., and whereby the coefficience .alpha., .beta., .gamma., and .delta.are weighing factors that are allocated to the individual picture element signals.
The publication "Architektur und Schaltkreistechnik in CMOS-ICs fur die DPCM-Codierung von Videosignalen" by Peter Pirsch in the Mitteilung des Forschungszentrums der SEL AG in Stutgart, pages 213-222, provides an overview of the principle of DPCM technology. A DPCM system having two-dimensional prediction and DPCM architecture solutions are presented. FIG. 5 of the cited publication sets forth a modified DPCM system having four-stage prediction error identification and a predictor. The time-critical path in this arrangement is merely composed of a subtractor, a quantizer and a register. Only further paths wherein two additions or one addition and one subtraction are required between two successive registers are present in addition to this path. For the reasons recited in the third paragraph of page 218, it is necessary to utilize a limiter function in the arrangement of FIG. 5 not within a loop but at the input side. In order to prevent overflows and under flows, the numerical range of the input signal is thus limited, this, however, being undesirable in many cases. The limiter function should only be activated for overflows or under flows arising in the DPCM arrangement.